This invention relates to a control system of the type wherein manual control devices such as a control sticks are provided which have an electro-simulated variable rate feel. In particular, the invention relates to a system having two control sticks such as are employed in aircraft, which are servo coupled in a manner coupling the motions as well as the applied forces of the users of the two control sticks.
Servo control technology is well developed as applied for use in the field of robotics. In particular, electrical motor and servo control systems have been developed and employed in the past in the design of robotic hand controllers which are capable of reflecting forces experienced at the robotic end, back to, for example, a human operator.
One example of the type of controller to which the present invention is directed is disclosed in U.S. Pat. No. 4,150,803, which teaches an operator control stick having an electro-simulated Variable rate feel system. The simulated feel system of the device of U.S. Pat. No. 4,150,803 provides the operator with proper force and feel characteristics when used to command a boom employed during refueling operations between aircraft in flight.
The types of controllers to which the invention is directed generally involve the use of a control stick actuatable in at least two mutually perpendicular planes to provide both vertical and lateral control of the device being controlled. This invention could be applied to controllers moveable in three rotational or three translational axes with up to six axes degrees of freedom. A position transducer is associated with the control stick and is used to generate output signals which command a control actuator to effect control of the device being controlled. The output from the transducer is also fed, typically, to at least one servo motor, which is mechanically coupled to an axis of the control stick. The servo motor either applies a resisting force on the control stick or, in response to a signal produced by sensors that detect forces applied to the device or surface being controlled, drives the stick and in turn, drives the device being controlled to alleviate forces generated by the device under control.
These types of controllers are particularly desirable for use in the operation of modern day aircraft, in particular, in the form of the control sticks or yokes. When employed in aircraft for use by pilots, it is desirable to provide two control sticks, one for use by the pilot and the other for use by the co-pilot.
In operation, the devices as used in the cockpit of aircraft are typically designed to exhibit some desired force versus displacement characteristics to the user whereby the magnitude of the control stick displacement is proportional to the force applied. The pilot controller produces as its output an electrical signal corresponding to the control stick position, and the signal is used to control the aircraft, through the action of various motors and mechanical means, in a manner which is well known to those of ordinary skill in the art and is conventional. Thus, with such systems there results and electronically controlled controller having force feel characteristics like those of purely mechanically linked systems. These applications in aircraft are typically referred to as "fly by wire" applications. Examples of presently existing applications of this technology are the systems employed in the Air Bus A320 Transport Aircraft, the General Dynamics F16 Fighter Aircraft and the NASA Space Shuttle.
When employed on aircraft, its is desirable to couple the two control sticks together to insure that they track each other and that only a single set of command signals are provided to the aircraft, for example, to the control surfaces and engines. In the past, aircraft pilot controllers had been coupled between pilot and co-pilot seats by mechanical means such as linkages, shafts, hydraulic devices and other complicated, bulky and weighty mechanisms. Recent efforts to save on the weight of these mechanical coupling systems have provided fly by wire designs which employ no means of coupling the motions of the pilot and co-pilot control sticks. The disadvantage of this approach is that it requires that some means of averaging or arbitrating between differing command signals, in the event that the pilot and co-pilot at the same instant move the controllers in opposite directions. Further, another disadvantage of such a system is that the forces versus displacement characteristics of the controllers are decoupled from the loading on the aircraft control surfaces and from the commands of the auto-pilot.
Accordingly, in the present invention, the disadvantages of having a decoupled pilot and co-pilot control system are avoided without requiring the heavy and bulky mechanical linkages or other such devices employed in the prior art.